Preeclampsia and eclampsia are toxemias associated with pregnancy. Preeclampsia is classically defined as the triad of hypertension, proteinuria, and edema associated with pregnancy. Other manifestations of preeclampsia are vascular prostenoid and platelet derangements, vasospasm, utero-placental vascular lesions, and in severe cases, convulsions and coma (eclampsia). Walsh et al., Am. J. Obstet. Gynecol., 151:100-15 (1985); Goodman et al., Am. J. Obstet. Gynecol., 142:817-22 (1982); Kitzmiller et al., Am. J. Obstet. Gynecol., 118:362-8 (1974); Giles et al., Br. J. Obstet. Gynecol., 88:1115-19(1981); and Gant et al., J. Clin Invest., 52:2682-89 (1973).
Toxemia occurs more often in women pregnant for the first time and in those over the age of thirty-five. Toxemia is especially frequent in patients with prior renal and vascular disease. A significant percentage of pregnant women with preexisting hypertension are also likely to have a toxemic episode.
A common histologic finding in toxemia is a marked swelling of the endothelial and epithelial cells of the glomeruli of the kidneys. A characteristic lesion in toxemia is deposition of fibrin in the glomeruli. Harrisons, Principles of Internal Medicine. 7th ed., McGraw Hill Co., pgs 1401-02, (1974). The onset of toxemia may be insidious or quite abrupt. Although toxemia generally occurs in the third trimester, it may also begin much earlier.
Although the combination of abnormalities associated with preeclampsia suggests that the disorder may result from progressive maternal and/or placental endothelial-vascular damage, the lack of specific markers for endothelial-vascular injury has prevented testing this hypothesis. A marker that correlates with the disease state and that indicates preeclampsia prior to clinical evidence of the disease would allow detection of preeclampsia early in the course of the disease when clinical intervention can be effective or possibly preventative.
Fibronectin, fibrinogen, antithrombin III, fibrin monomer, (.alpha.).sub.2 -antiplasmin, fibrinogen split products and D-dimer have been studied to determine their value as predictive markers. Elevated levels of total circulating (plasma) fibronectin, as compared with controls, have been observed in preeclamptic patients late in gestation. Stubbs et al., Am. J. Obstet Gvnecol., 150(7):885-87 (1984); Lazarchick et al., Am. J. Obstet Gynecol., 154(5):1050-53 (1986); and Saleh et al., Am. J. Obstet. Gynecol., 157 (2): 331-336, (1987). Fibronectin is an adhesive glycoprotein found in plasma and on cell surfaces and extracellular matrices. By binding other macromolecules as well as cells, fibronectin serves to promote anchorage of cells to substrata. Hynes, in Cell Biology of the Extracellular Matrix, Hay ed., Plenum Press, pages 295-334 (1982); Hynes et al., J. Cell Biol., 95:369-77 (1982). Fioronectin has been observed to accumulate at sites of tissue injury in vivo. Peters et al., Am. Rev. Resoir. Dis., 138:167-174, (1988).
Fibronectin is composed of subunits of variable primary structure [average relative molecular mass of 250 kilodaltons (kDa)]. The subunits are, disulfide-linked to form dimers or multimers derived from a pool of similar but nonidentical polypeptides. Hynes, in Cell Biology of the Extracellular Matrix, Hay ed., Plenum Press, pages 295-334 (1982); Hynes et al., Cell Biol., 95:369-77 (1982); Schwarzbauer et al., Proc. Natl., Acad. Sci. USA, 82:1424-28; Kornblihtr et al., EMBO J., 4(7): 1755-59 (1985). Thus, fibronectin refers to several species of glycoprotein, some of which are more fully characterized than others.
Two major fibronectin classes are plasma fibronectin and cellular fibronectin. Plasma fibronectin (pFn) is secreted by hepatocytes, whereas cellular fibronectin (cFn) is secreted by a variety of cultured cells including endothelial cells and fibroblasts. Jaffe et al., J. Exp Med., 147:1779-91 (1978); Birdwell et al., Biochem. Biophys. Res. Commun., 97(2):574-8 (1980). Despite extensive physical and immunologic similarities, the two classes of fioronectin differ in electrophoretic behavior, solubility, and biologic activities. Tamkun et al., J. Biol. Chem., 258 (7):4641-47 (1983); Yamada et al., J. Cell Biol., 80:492-98 (1979); Yamada et al., Biochemistry, 16 (25) 2552-59, (1977).
Primary structural differences between plasma and cellular fibronectins have been found by peptide mapping [Hayashi et al., J. Biol. Chem., 256(21):11,292-11,300 (1981)] cDNA cloning [Kornblihtt et al., Embo J., 4:1755-1759 (1985)] and immunologic techniques [Atherton et al., Cell, 25:133-41 (1981)]. From these data, it has been determined that the primary structure of fibronectin monomer contains three different types of internal repeats known as homology Types I, II and III, having length of about 40, 60 and 90 amino acids residues, respectively [Kornblihtt et al., Embo J., 4:1755-1759 (1985)]. All of the various distinct Fn moieties are produced by a single gene, with differences in primary structure resulting from alternative splicing of the primary mRNA transcript in at least three regions. Kornblihtt et al., EMBO J., 4(7):1755-59 (1985); Schwarzbauer et al., Proc. Natl. Acad. Sci. USA, 82:1424-28 (1985); Gutman et al., Proc. Natl. Acad. Sci. USA, 84:7179-82 (1987); Schwarzbauer et al., EMBO J., 6(9):2573-80, (1987).
A variable region corresponding to a single exon, encoding for exactly one 90 amino acid Type III structural repeat was identified in mRNA from human fibroblasts and two human tumor cell lines, but could not be detected in human hepatocyte mRNA. The region was termed EDI ("ED" for extra domain). Kornblihtt et al., EMBO J., 4(7):1755-59 (1985); Kornblihtt et al., EMBO J., 3(1):221-26 (1984); Kornblihtt et al., Nucleic Acids Res., 12(14):5853-68 (1984).
Since the vast majority of soluble Fn in the circulation is derived from hepatocytes [Tamkun et al., J. Biol. Chem., 258(7):4641-47 (1985)], pFn is believed to be composed primarily of dimers comprised of Fn monomers lacking the ED1 region (ED1-monomers). Peters et al., Amer. Rev. Reso. Dis., 138(1):167-74 (1988).
In contrast, the extra Type III repeat (ED1) was postulated to be a domain unique to cellular fibronectins. Shwarzbauer et al., Proc. Natl. Acad. Sci. USA, 82:1424-28 (1985); Kornblihtt et al., EMBO J. 3(1):221-26 (1984); Kornblihtt et al., Nucleic Acids Res. 12(14):5853-68 (1984). These cFns are produced by a variety of other cell types in the form of dimers or insoluble multimers, Schwarzbauer et al., EMBO J. 6(9):2573-80 (1987).
Recently Gutman et al., Proc. Natl. Acad. Sci. USA, 84:7179-82 (1987) reported a second region of Type III variability in human fibronectin that arises due to alternative RNA splicing. This region has been labelled ED2, for extra domain 2. The ED2 region is a 91 amino acid repeat having Type III homology and is located between the DNA- and the cell-binding domains of Fn as contrasted to the ED1 region located toward the C terminus of the molecule. Because hepatocytes are not known to produce mRNA having the variably included Type III sequences, both the ED1 and ED2 regions are restricted to cellular Fn.
Combination of all the possible patterns of splicing in these regions of variability can potentially lead to a large number of distinct Fn polypeptide monomers from a single gene. Schwarzbauer et al., EMBO J., 6(9):2573-80 (1987), reports that an additional Type III repeat of Fn (III-9) could also potentially be variably included through alternative splicing of Fn RNA in certain cell lines.